Disable caching repo-wide by creating a repo variable/secret

[bkeryan]

Problem to Solve

The setup-poetry caches the Poetry venv. It would be nice if there was a way to disable this without editing workflows.

#38 would also benefit from this.

Proposed Solution

Update the workflows to disable caching if a special variable is set to true.

AB#3354228

[szb640]

While looking at the how caching is implemented, I've come across post actions. We could setup a post action to run just before caching, that clears the Poetry venv directory when it wasn't grabbed from the cache (so it won't be present when saving the cache), and leave it to be cleaned by the post-job cleanup in other instances (when it was originally fetched from the cache, so caching will not occur). That way we can have caching without the venv dir.

[bkeryan]

Note that composite actions do not directly support post actions. To use post actions, we would have to either rewrite the composite action in Javascript or call another Javascript action that runs a post action on our behalf.